1. Field of the Invention
The present invention relates to a communication system and a method for enhancing network efficiency, and a computer program product therefor; specifically to a communication system and a method for enhancing network efficiency by way of dynamically adjusting a clear-to-send power, and a computer program product therefor.
2. Descriptions of the Related Art
Due to the progress of information technology and the development of communication medium in these years, network has become one of the inevitable communication mediums. Among them, wireless mash network (WMN) is an attractive approach for corporations, campuses, and locations that are not prone to establish wired networks because of its convenience of setting-up and widely usage range.
When packets are transmitted under the IEEE 802.11 protocol, collisions and unnecessary transmission suppressions occur frequently, wherein the unnecessary transmission suppressions are also known as the exposed-terminal problem. For example, referring to FIG. 1, when a first node 11 intends to transmit a first packet 12 to a second node 13, the first node 11 first transmits a request-to-send packet to the second node 13. The second node 13 responds a clear-to-send packet to the first node 11. The first node 11 then transmits the first packet 12 to the second node 13 after receiving the clear-to-send packet. The second node 13 finally transmits an acknowledge packet to the first node 11 to acknowledge the safe receipt and the process of a packet transmission is done. However, if a third node 15 is going to transmit a second packet 14 to a fourth node 17 at the time the first node 11 transmits the request-to-send packet to the second node 13, the third node 15 will temporarily stop transmitting a request-to-send packet to the fourth node 17 to prevent from collision since the third node 15, located in the signal coverage area 19 of the first node 11, is aware of the request-to-send packet transmitted by the first node 11. After the first node 11 finishes the transmission of the first packet 12, the transmission of the second packet 14 continues.
One can observe from FIG. 1 that the signal coverage area 16 of the third node 15 does not cover the second node 13. In other words, the transmission of the second data 14 from the third node 15 to the fourth node 17 does not affect the second node 13 to receive the first packet 12. That is, when the third node 15 transmits the second packet 14 to the fourth node 17, the transmission does not collide with the operations of the second node 13. Theoretically, the first packet 12 and the second packet 14 may be transmitted simultaneously. The exposed terminal problem degrades the usage rate of a network, reduces the total data amount of parallel transmission in a network, and, hence, wastes bandwidths.
One of the conventional solutions to the exposed terminal problem is to implant a GPS receiver in every node. When a node intends to transmit a packet, the node provides its location information obtained from the GPS receiver in a request-to-send packet and a receiving node also provides its location information in a clear-to-send packet. Consequently, other nodes can determine whether to suppress transmission according to the location information in the request-to-send packet and the clear-to-send packet. The total data amount of parallel transmission increases thereby. Nevertheless, obtaining location information through GPS receivers is costly, and GPS receivers have a distortion range of tens meters.
Accordingly, conventional solutions to the exposed-terminal problem are costly and inaccurate. A solution having advantages of no need of extra hardware and high accuracy to increase the total data amount of parallel transmission is still desired in this field.